The human body functions through a number of interdependent physiological systems controlled through various mechanical, electrical, and chemical processes. The metabolic state of the body is constantly changing. For example, as exercise level increases, the body consumes more oxygen and gives off more carbon dioxide. The cardiac and pulmonary systems maintain appropriate blood gas levels by making adjustments that bring more oxygen into the system and dispel more carbon dioxide. The cardiovascular system transports blood gases to and from the body tissues. The respiration system, through the breathing mechanism, performs the function of exchanging these gases with the external environment. Together, the cardiac and respiration systems form a larger anatomical and functional unit denoted the cardiopulmonary system.
The cardiopulmonary system is controlled by the sympathetic and parasympathetic nervous systems. Some organs receive innervation from both the sympathetic and parasympathetic nervous systems, and in some of these organs, the impulse discharge from this dual innervation exerts antagonistic effects, so that the amount of activity depends on the balance between the discharges over the two autonomic outflows. The balance between the sympathetic and parasympathetic nervous systems is denoted the autonomic balance.
The innervation of the natural pacemaker of the heart exhibits an antagonistic autonomic balance. The heart receives excitatory innervation from the sympathetic outflow of the upper four or five thoracic segments, which acts on the sinoatrial pacemaker node, the atrioventricular conduction system, the atrial and ventricular myocardium, and the coronary vessels. Excitation from this outflow accelerates the heart rate and increases the force of cardiac contraction.
The parasympathetic innervation originates from the medulla oblongata in the vicinity of the dorsal motor nucleus of the vagus and the nucleus ambiguous, and this influence is exerted on the sinoatrial and atrioventricular nodes and the atrial myocardium. Excitation from this output decelerates the heart rate. When the impulse discharge of the sympathetic system dominates, the heart rate accelerates, but when the parasympathetic system is dominant, the heart rate slows.
Autonomic imbalances have been implicated in a wide variety of pathologies, including depression, fatigue, premenstrual syndrome, hypertension, diabetes mellitus, ischemic heart disease, coronary heart disease and environmental sensitivity. Stress and emotional states have been shown to dramatically affect autonomic function.
Autonomic imbalances and other disorders may affect the cardiovascular, respiratory, and other physiological systems. For example, heart failure (HF) is a clinical syndrome that impacts a number of physiological processes. Heart failure is an abnormality of cardiac function that causes cardiac output to fall below a level adequate to meet the metabolic demand of peripheral tissues. Heart failure is usually referred to as congestive heart failure (CHF) due to the accompanying venous and pulmonary congestion. Congestive heart failure may have a variety of underlying causes, including ischemic heart disease (coronary artery disease), hypertension (high blood pressure), and diabetes, among others.
There are a number of diseases and disorders that primarily affect respiration, but also impact other physiological systems. Emphysema and chronic bronchitis are grouped together and are known as chronic obstructive pulmonary disease (COPD). Pulmonary system disease also includes tuberculosis, sarcoidosis, lung cancer, occupation-related lung disease, bacterial and viral infections, and other conditions.
Chronic obstructive pulmonary disease generally develops over many years, typically from exposure to cigarette smoke, pollution, or other irritants. Over time, the elasticity of the lung tissue is lost, and the lungs become distended, unable to expand and contract normally. As the disease progresses, breathing becomes labored, and the patient grows progressively weaker.
Disordered breathing is a respiratory system condition that affects a significant percentage of patients between 30 and 60 years. Disordered breathing, including apnea and hypopnea, may be caused, for example, by an obstructed airway, or by derangement of the signals from the brain controlling respiration. Sleep disordered breathing is particularly prevalent and is associated with excessive daytime sleepiness, systemic hypertension, increased risk of stroke, angina, and myocardial infarction. Disordered breathing can be particularly serious for patients concurrently suffering from cardiovascular deficiencies.
Various types of disordered respiration have been identified, including, apnea (interrupted breathing), hypopnea (shallow breathing), tachypnea (rapid breathing), hyperpnea (heavy breathing), and dyspnea (labored breathing). Combinations of the respiratory cycles described above may be observed, including, for example, periodic breathing and Cheyne-Stokes respiration (CSR). Cheyne-Stokes respiration is particularly prevalent among heart failure patients, and may contribute to the progression of heart failure.